1. Field of the Invention
The present invention is generally in the field of electrical circuits and systems. More specifically, the present invention is in the field of power management circuits and systems.
2. Background Art
The storage and on-demand delivery of electrical energy is becoming increasing important as the shift from fossil fuel based technologies to green technologies gains momentum. Gas/electric hybrid automobiles, for example, typically utilize arrays of secondary batteries that are alternately charged and discharged in response to vehicular operation. Those secondary battery packs may constitute a substantial portion of the cost of a gas/electric hybrid vehicle, and their performance, and in particular their longevity, may significantly influence consumer willingness to invest in the initially costlier vehicle purchase price.
Typical energy storage packs are assembled from individual batteries or energy cells and each energy cell unit is often assumed or selected to be nominally identical. In practice, the batteries or other energy cells will have individual performance parameters, such as storage capacity and/or resistance, that vary somewhat from energy cell to energy cell. The distribution or variation among energy cells may arise, for example, from process variation at the time of manufacturing, from unequal wear during use cycles, and through other non-use related degradation of the energy cells. In general, the distribution of the variations is often seen to grow wider as the energy cells grow older. Unfortunately, the longevity and capacity of a group of energy cells used collectively, such as a battery pack, is typically determined by the weakest energy cell or battery in the group.
Conventional approaches to providing management of energy cell performance tend to focus on balancing one aspect of the energy cells at a particular time, for example, when a battery pack is not in use, or near the end of a charge or discharge cycle. At that time, for example, the stronger cells may be drained down to the state of charge (SOC) of the weakest cell. In other implementations, circuitry may be provided to transfer charge from one cell to an adjacent cell until energy cell balance is achieved. A significant challenge faced by existing balancing approaches is the increasingly high voltages supplied by the battery packs utilized in industrial and automotive applications. Even when active balancing is attempted, for example, the components used in the balancing circuitry must typically tolerate the full bus voltage of the battery pack, rendering those active balancing solutions costly to implement.
Thus, there is a need to overcome the drawbacks and deficiencies in the art by providing a cost effective active power balancing solution capable of maintaining charge balance during dynamic operation.